The invention describes a power transmission system and, more particularly, to a distributed energy resource system enhanced to provided supplemental current when required to a power distribution.
Distributed energy resource (DER) systems consist of energy generation and storage systems placed at or near a power load center. Unlike large electric power plants, DERs are small in terms of capacity and are installed close to the consumer. Examples of DERs are fuel cells, microturbines and photovoltaic systems. These distributed resources can provide the consumer with better power quality and higher energy efficiency. A DER system also has the potential to mitigate transmission congestion, control price fluctuation, strengthen security and improve grid stability. Most DER systems are typically less than a megawatt in size. Such a limitation will degrade DER's transient roadability in case of large load switching, such as induction motor starting. Therefore, it is highly desirable to integrate a supplemental power conversion system (SPCS) into a DER system so that the over-loaded energy can be compensated by injecting supplementary current from a SPCS into the grid. A device is required which senses the DER current to detect the overload condition and triggers the SPCS inverter.
The implementation of distributed energy resource systems as a supplementary or stand-alone power source can achieve significant benefits in terms of economy and reliability, such as better power quality, higher energy efficiency and improved system stability. However, an isolated DER system will experience overload stress when transient inductive loads, such as motor starting, drawing excessive currents from the system. Such stress might cause severe voltage sag due to the over-current protection of the DER system itself. In many cases, the system protection scheme will shut down the DER system if the current is much higher than the DER system capability.
Required is a system and method for implementing a distributed energy resource system that has suitable capability to supply excess current demands and protect the integrity of the energy delivery system.